1. Field of the Invention
The present disclosure relates generally to network switching, and more particularly to an adaptive spanning tree protocol that allows multiple spanning tree instances to be dynamically modified based on selected traffic attributes.
2. Description of Related Art
Spanning Tree Protocols (STPs) are used in computer networks to maintain a reconfigurable-on-failure loop-free network topology within a group of interconnected switches having redundant paths. In the original STP specification (IEEE 802.1D, published by the Institute of Electrical and Electronic Engineers), failover and fallback of links to employ alternate paths was timer-based.
Enhancements to the core spanning tree protocol were suggested, allowing rapid convergence and recovery of the spanning tree after link failure, independent of any timer. These enhancements became known as the Rapid Spanning Tree Protocol (RSTP), described in the IEEE 802.1w specification, currently merged into the IEEE 802.1D-2004 standard.
Further enhancements to the basic spanning tree protocol were made to allow a group of switches to run multiple spanning trees instances within the same spanning tree domain. An administrator provisions each switch in the spanning tree domain with a mapping between spanning tree instances and VLANs (Virtual Local Area Networks), and tailors the bridge parameters in each switch so that different multiple spanning tree instances will converge to different least cost paths through the network. The traffic for each VLAN is forwarded along the network paths for the spanning tree instance mapped to that VLAN. With some effort, an administrator can therefore achieve better load balancing than is generally possible with a single spanning tree instance, since no operational port will necessarily be blocked in all spanning tree instances. These enhancements are described in the IEEE 802.1s standard as the “Multiple Spanning Tree Protocol” (MSTP). Currently, MSTP has been integrated into the IEEE 802.1Q-2003 standard.
Additional enhancements in the field of spanning tree design are described in U.S. patent application Ser. No. 11/065,724, entitled “Packet Attribute-Mapped Spanning Tree Protocol,” filed Feb. 24, 2005, and incorporated herein by reference. The Attribute-Mapped Spanning Tree Protocol (AMSTP) can be configured to map packet attributes other than (or in addition to) VLAN identifier to logical spanning tree instances. For instance, different spanning trees can be associated with different Ethernet layer 2 header Ethertypes, layer 3 addresses or portions of addresses, layer 4 types indicated by layer 3, IP options, multicast/unicast traffic, higher-layer header attributes, data attributes for specific packet types, etc. This structure provides powerful flexibility for dividing network resources according to a wide variety of specific traffic attributes.